<template>
  <div class="countTo-container">
    <span class="countTo-content">
      {{ displayValue }}
    </span>
  </div>
</template>

<script>
import { requestAnimationFrame, cancelAnimationFrame } from './requestAnimationFrame.js'
export default {
  name: 'index',
  props: {
    startVal: {
      type: Number,
      required: false,
      default: 0,
    },
    endVal: {
      type: Number,
      required: false,
      default: 2017,
    },
    duration: {
      type: Number,
      required: false,
      default: 3000,
    },
    autoplay: {
      type: Boolean,
      required: false,
      default: true,
    },
    decimals: {
      type: Number,
      required: false,
      default: 0,
      validator(value) {
        return value >= 0
      },
    },
    decimal: {
      type: String,
      required: false,
      default: '.',
    },
    separator: {
      type: String,
      required: false,
      default: ',',
    },
    prefix: {
      type: String,
      required: false,
      default: '',
    },
    suffix: {
      type: String,
      required: false,
      default: '',
    },
    useEasing: {
      type: Boolean,
      required: false,
      default: true,
    },
    easingFn: {
      type: Function,
      default(t, b, c, d) {
        return (c * (-Math.pow(2, (-10 * t) / d) + 1) * 1024) / 1023 + b
      },
    },
  },
  data(){
    return{
      localStartVal: this.startVal,
      displayValue: this.formatNumber(this.startVal),
      printVal: null,
      paused: false,
      localDuration: this.duration,
      startTime: null,
      timestamp: null,
      remaining: null,
      rAF: null,
    }
  },
  computed: {
    countDown() {
      return this.startVal > this.endVal
    },
  },
  watch: {
    startVal() {
      if (this.autoplay) {
        this.start()
      }
    },
    endVal() {
      if (this.autoplay) {
        this.start()
      }
    },
  },
  mounted() {
    if (this.autoplay) {
      this.start()
    }
    this.$emit('mountedCallback')
  },
  methods:{
    start(){
      this.localStartVal = this.startVal
      this.startTime = null
      this.localDuration = this.duration
      this.paused = false
      // requestAnimationFrame返回的是一个代表任务ID的整数值, 用于取消动画
      // requestAnimationFrame使用一个回调函数作为参数。这个回调函数会在浏览器重绘之前调用。
      this.rAF = requestAnimationFrame(this.count)
    },
    // 暂停或恢复
    pauseResume(){
      if(this.paused){
        this.resume()
        this.paused = false
      }else{
        this.pause()
        this.paused = true
      }
    },
    // 暂停
    pause(){
      cancelAnimationFrame(this.rAF)
    },
    // 恢复
    resume(){
      this.startTime = null
      this.localDuration = +this.remaining
      this.localStartVal = +this.printVal
      requestAnimationFrame(this.count)
    },
    // 重置
    reset(){
      this.startTime = null
      cancelAnimationFrame(this.rAF)
      this.displayValue = this.formatNumber(this.startVal)
    },
    count(timestamp){
      if(!this.startTime) this.startTime = timestamp
      this.timestamp = timestamp
      const progress = timestamp - this.startTime   // 剩余动画时间
      this.remaining = this.localDuration - progress
      if(this.useEasing){
        if(this.countDown){  // 未达到最终值
          this.printVal = this.localStartVal - this.easingFn(progress, 0, this.localStartVal - this.endVal, this.localDuration)
        }else{
          this.printVal = this.easingFn(progress, this.localStartVal, this.endVal - this.localStartVal, this.localDuration)
        }
      }else{
        if(this.countDown){ // 未达到最终值
          this.printVal = this.localStartVal - (this.localStartVal - this.endVal) * (progress / this.localDuration)
        }else{
          this.printVal = this.localStartVal + (this.endVal - this.localStartVal) * (progress / this.localDuration)
        }
      }
      if(this.countDown){
        this.printVal = this.printVal < this.endVal ? this.endVal : this.printVal
      }else{
        this.printVal = this.printVal > this.endVal ? this.endVal : this.printVal
      }
      this.displayValue = this.formatNumber(this.printVal)
      if(progress < this.localDuration){
        this.rAF = requestAnimationFrame(this.count)
      }else{
        this.$emit('callback')
      }
    },
    isNumber(val){
      return !isNaN(parseFloat(val))
    },
    formatNumber(num){
      num = num.toFixed(this.decimals)
      num += ''
      const x = num.split('.')
      let x1 = x[0]
      const x2 = x.length > 1 ? this.decimal + x[1] : ''
      const rgx = /(\d+)(\d{3})/
      if(this.separator && !this.isNumber(this.separator)){
        while(rgx.test(x1)){
          x1 = x1.replace(rgx, '$1' + this.separator + '$2')
        }
      }
      return this.prefix + x1 + x2 +this.suffix
    },
    destroyed(){
      cancelAnimationFrame(this.rAF)
    },
  },
}
</script>

<style lang="scss" scoped>
.countTo-container{
  height: 100px;
  line-height: 100px;
}
.countTo-content{
  font-size: 24px;
}
</style>
